RFR: 8338731: MemoryLayout::offsetHandle can return a negative offset
Per Minborg
pminborg at openjdk.org
Fri Aug 23 14:04:03 UTC 2024
On Wed, 21 Aug 2024 13:26:58 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:
> When working on startup improvements, I noticed that the method handle returned by `MemoryLayout::offsetHandle` can overflow if the client calls the handle with a base offset that is too big.
>
> In other similar situations, the layout API always fails with `ArithmeticException` (see `MemoryLayout::scale`), so we should do the same here.
>
> The fix is to use a `Math::addExact(long, long)` for the outermost add operation in the computation of the offset method handle. That outermost computation in fact is the only one that can overflow: it is an addition between a user-provided base offset `B` and a layout offset `L`. `L` is guaranteed not to overflow, by construction (as `L` is derived from a layout path). But `B` + `L` might overflow, so the new logic checks for that.
Nice catch.
Unrelated: I wonder if the performance of:
MH_ADD = lookup.findStatic(Long.class, "sum",
MethodType.methodType(long.class, long.class, long.class));
and
MH_ADD = MethodHandles.publicLookup().findStatic(Long.class, "sum",
MethodType.methodType(long.class, long.class, long.class));
Differ?
-------------
Marked as reviewed by pminborg (Reviewer).
PR Review: https://git.openjdk.org/jdk/pull/20662#pullrequestreview-2257329578
PR Comment: https://git.openjdk.org/jdk/pull/20662#issuecomment-2307163178
More information about the core-libs-dev
mailing list